The field of the invention is oxide-boride ceramic bodies which can have one or more of oxide phases and one or more of boride phases.
Most commonly heretofore, these oxide-boride ceramic bodies have been of the type physically formed of ingredients corresponding to the crystalline phases in the ceramic bodies. By way of exemplary illustration, reference is made to the following prior art documents. U.S. Pat. No. 2,270,607 discloses mixing, shaping and sintering at least 10 wt. % of oxides of Al, Zr, Be and/or Th with borides of W, Fe and the like to yield ceramic bodies of those same phases. U.S. Pat. No. 3,067,146 discloses hot pressing or shaping and sintering of mixtures of TiB.sub.2, Al.sub.2 O.sub.3 and Cr.sub.2 O.sub.3 to form ceramic bodies of substantially those same phases. U.S. Pat. No. 3,296,002 discloses firing porous shaped mixtures of aluminum and alloys thereof with borides of Cr, Mo, Ti, W and Zr in oxidizing atmosphere to form porous alumina-boride ceramics. U.S. Pat. No. 4,022,584 discloses hot pressed or shaped and sintered mixtures of Al.sub.2 O.sub.3, MgO and borides of metal from Groups 4b, 5b and 6b to provide ceramic bodies of substantially those same phases. U.S. Pat. No. 4,110,260 sintering shaped mixtures of a wide variety of ingredients including insulating ceramics such as alumina and zirconia and electroconductive substances such as borides of Ti and Zr. U.S. Pat. No. 4,343,909 discloses sintering pressed mixtures of Al.sub.2 O.sub.3, ZrO.sub.2, TiB.sub.2 and grain growth inhibitor to yield a product of substantially those same phases.
Generally those hot pressed or sintered physical mixtures require heating to relatively high temperatures of 1600.degree.-2000.degree. C. or so. Moreover, such ceramic bodies have properties which are dependent upon and limited by the inherent effects of the physical nature of their ingredients which are physically combined. The distribution and sizing of the phases are generally directly related to the particle sizing and mixing of ingredient powders. The powders are not always easily available in uniformly fine sizes for obtaining homogeneous distribution of phases and superior properties. Milling of powders to improve their sizing can lead to undesirable situations. In fact, some powders such as TiB.sub.2 in sizes of about 5 .mu.m or finer present fire and explosion hazard during milling due to their rapid reaction with oxygen in air under conditions of frictional heating.
Amongst numerous reactions for forming other types of multiphase bodies by an unusual reaction hot pressing process involving passage of electric current through the reaction mixture during the process, U.S. Pat. No. 3,143,413 discloses reaction hot pressed ceramics with phases of MgO and either TiB.sub.2 or ZrB.sub.2, but no details are given about the properties of such body made from -60 mesh reactant powders heated up to 1800.degree.-2300.degree. C.
There has been a continuing need for oxide-boride ceramics with easily controlled and predictable composition, crystal structure (including uniform phase distribution and fine grain size) and related physical properties, and which can be easily and economically fabricated in a variety of shapes by heating at lower temperatures.